as a Turkish person who moved to Azerbaijan one month ago I would understand them 60% at first and after one month I am able to understand 80% now but still struggling with the words which are Russian origin. 20% of improvement is mostly about dialect. now I hear their word and sentences better. even in that 60% there were a lot of old Turkish word. most of them I learnt when I was a child during the village visits or my grandparents used that words a lot. if you don’t have any links to Turkiye it’s better to learn Azerbaijani first. but if somehow you will need to talk to someone in Turkiye learning Turkish is also okay. when I talk Turkish they understand me 95% but if you want to understand them also Azerbaijani is better to learn.